Repeatability and Reproducibility of Photoreceptor Density Measurement in the Macula Using the Spectralis High Magnification Module

PURPOSE To evaluate the repeatability and reproducibility of photoreceptor density assessment in healthy subjects imaged with the Heidelberg Spectralis High Magnification Module (HMM) with manual cell counting. DESIGN Precision study, evaluation of diagnostic test or technology. PARTICIPANTS Eleven eyes of eight subjects. METHODS Images were acquired using the Spectralis HMM by a single operator during two separate imaging sessions. The three highest-quality images of each eye from each session were selected for analysis and co-registered. For a subset of patients, a second operator acquired images in one session, and images with best quality were selected for analysis. Photoreceptor densities were obtained by manual counts in squares of 0.0625 mm2 located in the parafovea. Repeatability (intragrader and intrasession) and reproducibility (interoperator, intergrader and intersession) were assessed by calculating the intra-class correlation coefficient (ICC) from linear mixed effects models. Bland-Altman plots, coefficients of repeatability and Pearson's correlation results were reported. MAIN OUTCOME MEASURES Intragrader, intrasession, intersession, interoperator and intergrader ICC estimates, and its 95% confidence intervals, for photoreceptor density measurements in the parafovea. RESULTS Twenty-four eyes of thirteen healthy subjects were initially imaged. Of these, eleven eyes (45.83%) of eight subjects that had at least three acceptable images in each session were included in this study. Mean parafoveal photoreceptor density was 14,988 cells/mm2 (SD = 1403.15). Intragrader ICC was 0.84 (95% CI: 0.57, 0.95), intrasession ICC was 0.69 (95% CI: 0.17, 0.86), intersession ICC was 0.88 (95% CI: 0.53, 0.96), interoperator ICC was 0.70 (95% CI: 0, 0.95) and intergrader ICC was 0.22 (95% CI: 0, 0.71). CONCLUSION Images obtained with the HMM allow for photoreceptor mosaic visualization in the macular area, mainly in the parafovea. Although densities obtained are in accordance with other reported methods in the literature, variability within and between images of the apparent cell mosaic were observed and this study did not demonstrate high repeatability and reproducibility for quantitative assessments using the manual counting method.